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    <meta charset="UTF-8">
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    <title>Document</title>
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<body>
    <script>
        //用户输入年份 输出当年月份2月份的天数
        function backDay() {
            let year = prompt('请输入');
            let flag = isLeapYear(year);
            if (flag) {
                console.log(year + '是闰年,2月份有29天');
            } else {
                console.log(year + '是闰年,2月份有28天');
            }
        }
        //单独抽取 判断闰年函数
        function isLeapYear(year) {
            let result = false;
            if ((year % 4 == 0) && year % 100 != 0 || (year % 100 == 0) && (year % 400 == 0)) {
                console.log(year + '是闰年');
                result = true;
            }
            return result;
        }
        //调用函数名·
        backDay();
    </script>
</body>

</html>